The present invention relates to digital recording and more particularly, to such recording with improved pulse rise time.
Digital record amplifiers used in helical-scan recording in the prior art as shown in FIG. 1 suffer from several problems. A source of digital information 10 is coupled to a record amplifier 12. The information is shown in FIG. 2A and the output of amplifier 12 in FIG. 2B. A rotating head 16 is coupled to stationary record amplifier 12 through a rotary transformer 14. As shown in FIG. 2C this prior art arrangement suffers from loss of timing integrity, loss of rise-time, and inability to handle data patterns containing large amounts of D.C. such as may be present in NRZ (non-return-to-zero) coding, which coding has the highest tape packing density. These problems become worse on playback due to tape jitter, thereby making bit detection difficult. Since all of these problems stem from the fact that the record amplifier is transformer coupled to the head, the problems can be overcome by eliminating the transformer coupling.
One way of eliminating the transformer coupling is to use slip rings. However such rings wear out, and may, together with their associated brushes, create excessive noise.
It is therefore desirable to have a digital recording system that can record using a code that has a large DC content, minimizes loss of timing integration and rise time, has a minimum of components that wear out and does not create noise.